1. Field of the Invention
This invention relates to a process for preparing fully drawn bicomponent fibers at high speeds and, more particularly, to a process of extruding two polyesters from a spinneret, passing the fibers through a cooling gas, drawing, heat-treating, and winding up the fibers at high speeds.
2. Description of Background Art
Synthetic bicomponent fibers are known. U.S. Pat. No. 3,671,379 discloses such fibers based on poly(ethylene terephthalate) and poly(trimethylene terephthalate). The spinning speeds disclosed in this reference are uneconomically slow. Japanese Patent Application Publication JP11-189923 and Japanese Patent JP61-32404 also disclose the use of copolyesters in making bicomponent fibers. U.S. Pat. No. 4,217,321 discloses spinning a bicomponent fiber based on poly(ethylene terephthalate) and poly(tetramethylene terephthalate) and drawing it at room temperature and low draw ratios. Such fibers, however, have low crimp levels, as do the polyester bicomponent fibers disclosed in U.S. Pat. No. 3,454,460.
Several apparatuses and methods have been proposed for melt-spinning partially oriented monocomponent fibers at high speeds, as disclosed in U.S. Pat. Nos. 4,687,610, 4,691,003, 5,034,182, and No. 5,824,248 and in International Patent Application WO95/15409. Generally, in these methods a cooling gas is introduced into a zone below the spinneret and accelerated in the travel direction of the newly formed fibers. However, such fibers do not crimp spontaneously and, therefore, do not have desirable high stretch-and-recovery properties.
An economical process for making highly crimpable polyester bicomponent fibers is still needed.
The process of the present invention for preparing fully drawn crimped bicomponent fibers, having after-heat-set crimp contraction values above about 30%, comprises the steps of:
(A) providing two compositionally different polyesters;
(B) melt-spinning the two polyesters from a spinneret to form at least one bicomponent fiber;
(C) providing at least one flow of gas to at least one quench zone below the spinneret and accelerating the gas flow to a maximum velocity in the direction of fiber travel;
(D) passing the fiber through said zone(s);
(E) withdrawing the fiber at a withdrawal speed such that the ratio of the maximum gas velocity to the withdrawal speed is so chosen to achieve a specific draw ratio range;
(F) heating and drawing the fiber at a temperature of about 50-185xc2x0 C. at a draw ratio of about 1.4-4.5;
(G) heat-treating the fiber by heating it to a temperature sufficient to result in an after-heat-set contraction value above about 30%; and
(H) winding up the fiber at a speed of at least about 3,300 meters per minute.
Another process of the present invention for preparing fully drawn bicomponent fibers, having after-heat-set crimp contraction values above about 30%, comprises the steps of:
(A) providing poly(ethylene terephthalate) and poly(trimethylene terephthalate) polyesters having different intrinsic viscosities;
(B) melt-spinning said polyesters from a spinneret to form at least one bicomponent fiber having either a side-by-side or eccentric sheath core cross-section;
(C) providing a flow of gas to a quench zone below the spinneret;
(D) passing the fiber through the quench zone;
(E) withdrawing the fiber;
(F) heating and drawing the fiber to a temperature of about 50-185xc2x0 C. at a draw ratio of about 1.4-4.5;
(G) heat-treating the fiber by heating it to a temperature sufficient to result in an after-heat-set contraction value above about 30%; and
(H) winding up the fiber at a speed of at least about 3,300 meters per minute.
The bicomponent fiber of this invention is of about 0.6-1.7 dtex/filament, the fiber having after-heat-set crimp contraction values of at least 30% and comprising poly(trimethylene terephthalate) and a polyester selected from the group consisting of poly(ethylene terephthalate) and copolyesters of poly(ethylene terephthalate), having a side-by-side or eccentric sheath core cross-section and a cross-sectional shape which is substantially round, oval or snowman.